Interest in fuel cell batteries as power sources for portable electronic devices has grown. A fuel cell is an electrochemical cell that uses materials from outside the cell as the active materials for the positive and negative electrode. Because a fuel cell does not have to contain all of the active materials used to generate electricity, the fuel cell can be made with a small volume relative to the amount of electrical energy produced compared to other types of batteries.
Fuel cells can be categorized according to the type of electrolyte used, typically one of five types: proton exchange membrane fuel cell (PEMFC), alkaline fuel cell (AFC), phosphoric-acid fuel cell (PAFC), solid oxide fuel cell (SOFC) and molten carbonate fuel cell (MCFC). Each of these types of fuel cell can use hydrogen and oxygen as the active materials of the fuel cell negative electrode (anode) and positive electrode (cathode), respectively. Hydrogen is oxidized at the negative electrode, and oxygen is reduced at the positive electrode. Ions pass through an electrically nonconductive, ion permeable separator and electrons pass through an external circuit to provide an electric current.
In some types of hydrogen fuel cells, hydrogen is formed from a hydrogen-containing fuel supplied to the negative electrode side of the fuel cell. In other types of hydrogen fuel cells, hydrogen gas is supplied to the fuel cell from a source outside the fuel cell.
A fuel cell system can include a fuel cell battery, including one or more fuel cells (e.g., a fuel cell stack), and a fuel source, such as a fuel tank or a hydrogen generator. Hydrogen generators that supply hydrogen gas to a fuel cell can be an integral part of a fuel cell system, or they can be removably coupled to the fuel cell system. A removable hydrogen generator can be replaced with another one when the hydrogen producing reactants have been consumed. Removable hydrogen generators can be disposable (intended for only a one-time use). Both removable and permanently installed hydrogen generators can be refillable (intended for use multiple times) to replace consumed reactant materials.
Hydrogen generators can produce hydrogen using a variety of reactants and a variety of methods for initiating the hydrogen generating reactants. Hydrogen gas can be evolved when a hydrogen containing material reacts. Examples of hydrogen containing materials include liquid or gaseous hydrocarbons (such as methanol), hydrides (such as metal hydrides and chemical hydrides), alkali metal silicides, metal/silica gels, water, alcohols, dilute acids and organic fuels (such as N-ethylcarbazone and perhydrofluorene). A hydrogen containing compound can react with another reactant to produce hydrogen gas, when the reactants are mixed together, in the presence of a catalyst, heat or an acid, or a combination thereof. A hydrogen containing compound can be heated to evolve hydrogen in a thermochemical decomposition reaction.
In selecting reactants for use in a hydrogen generator, consideration may be given to the following: (a) stability during long periods of time when the hydrogen generator is not in use, (b) ease of initiation of a hydrogen generating reaction, (c) the amount of energy that must be provided to sustain the hydrogen generating reaction, (d) the maximum operating temperature of the hydrogen generating reaction, and (e) the total volume of hydrogen that can be produced per unit of volume and per unit of mass of the reactant(s).
Reactants that can undergo thermal decomposition reactions to produce hydrogen gas are desirable because they generally produce a relatively high volume of hydrogen gas on a volumetric basis. Resistive electric heating elements can be used to provide the necessary heat to initiate the hydrogen producing reaction. Reactants can be contained in replaceable fuel units, which can be enclosed in packages. Therefore, to initiate the reaction, heat from external heating elements or electricity to operate internal heating elements must be conducted into the package. One way to accomplish this is through electrically and/or thermally conductive areas on the package. It may be desirable to heat only a limited portion of the reactant in a fuel unit at one time. This can be facilitated by having a separate electrically and/or thermally conductive area in the package associated with each of several portions of the reactant.
An object of the present invention is to provide a method for making a package for a hydrogen generator fuel unit that has one or more electrically conductive and/or thermally conductive areas in the package. It is desirable for the package to have a simple design, be made of a limited number of inexpensive materials and components and be manufactured easily and economically. A further object of the invention is to provide a method of making a fuel unit including the package and a hydrogen generator including the fuel unit.